Question: Suppose the area of a circle is ${9\pi}$. What is its circumference?
Solution: ${K = 9\pi}$ ${c = 6\pi}$ First, find the radius: $K = \pi r^2$ , so $r = \sqrt{K / \pi} = \sqrt{{9\pi} / \pi} = {3}$ Now find the circumference: $c = 2\pi r = 2\pi \cdot {3} = {6\pi}$.